Electron discharge tube



Feb. 6, 1934. J. H. JONKER Er AL ELECTRON DISCHARGE TUBE Filed May 14,1932 ATTORNEY Patented Feb. 6, 1934 UNITED STATES ELECTRON DISCHARGETUBE Johan Lodewyk Hendrik Junker and Karel Marinus Van Gessel,Eindhoven, Netherlands, as-

signors to Radio Corporation poration of Delaware of America, a cor-Application May 14, 1932, Serial No. 611,272, and

in Germany May 1, 1931 .2 Claims. (o1. 25o z7.5)

The invention relates to electron discharge tubes and more particularlyto tubes comprising an indirectly heated cathode. Such a cathodecommonly consists of a cylindrical metal body,

the cathode body proper, within which is arranged the heater which mayconsist of a hairpin-shaped wire of refractory material such, forexample, as tungsten. The cathode body usually consists of a nickelcylinder which surrounds the heater at some distance, if desired withthe interposition ofan insulating material, and the outer surface ofwhich is covered with a strongly electron emitting layer, for example,with barium oxide. It is usual to mount a cathode thus constructedwithin the tube with the aid of supports secured to the upper end and tothe lower end of the cathode body. Oneof these supports maysimultaneously to the cathode.

It has been demonstrated that the operation of a discharge tubecomprising such a cathode entails inconveniences substantiallyconsisting in a very non-uniform emission. Now it has been found thatthis must be ascribed to the fact that the temperature at differentpoints of the surface of the cathode body is non-uniform. Morepartlcularly the ends of this body have a considerably lower temperaturethan other points of the surface. It has been found that this resultsfrom the dissipation of heat which takes place at the ends of thecathode body for at these points the cathode is connected to supports orto current supply conductors.

The invention has for its object to remove this drawback by a plainconstruction of an electric discharge tube comprising an indirectlyheated cathode.

An electron discharge tube according to the invention comprises anindirectly heated cathode, he heater and the cathode body of which areso shaped that the amount of heat developed per unit of the cathodesurface by that portion of the heater which is located in theneighborhood of a point at which the cathode is supported, is largerthan the amount of heat developed per unit of the cathode surface by aportion of the heater which is not located in the neighborhood of apoint of support of the cathode. It is possible to obtain in this mannera uniform or substantially uniform distribution of the temperature overthe whole surface of the cathode, which results in a better emissionthan with the indirectly heated cathode hitherto used.

It is advantageous to constitute the cathode body by a small tube and togive the tube portion located in the neighborhood of the points ofsupport a smaller diameter than the other por tion. This portion locatedin the neighborhood of a point of support may be given for this purpose,for example, the shape of a cone.- Very satisfactory results areobtained by giving a portion of the heater of the cathode which islocated in the neighborhood of a point of support per unit of length ofthe cathode a greater length than a portion of'this heater which isnot'located in the neighborhood of a pointof support; -Very good resultsmay also be obtained by giving the heater and the points located in theneighborhood of a point of support of the cathode a higher resistancethan the points of this heater which are not located in theneighborhood-of a point of support of the cathode. found that with theseconstructions a substantially uniform temperature of the cathode bodycan always be obtained.

By the amount of heat produced by a determined portion of the heater perunit of the oathode surface is meant this: a portion limited by twoparallel planes perpendicular to the longitudinal axis of the cathodemust be assumed to be removed from the latter. To this cathode portionthere corresponds a determined portion of the heater. When the heater istraversed by a current, a certain amount of heat will be developed inthis portion of the heater. The cathode portion under consideration hasa certain emitting surface the size of which can be determined. Whendetermining the quotient of the amount of heat produced and the size ofthis surface, one obtains an amount of heat which is produced by theheater portion under consideration per unit of the cathode surface. Itis evident that this quotient depends on the intensity of the currentflowing through the heater. The quotient valid for a determined cathodeportion of the cathode may directly be compared with the quotient foundfor another cathode portion because one may start in this case from thesame current intensity in the whole heater.

The invention will be by referring to the which,

Figure 1 represents one embodiment of a discharge tube according to theinvention;

Figure 2 represents the cathode utilized in this tube,

Figures 3 and 4 are and Figure 5 is another form according to theinvention.

more clearly understood accompanying drawing in of cathode structure Ithas been sections of this cathode,

In Figure 1, 1 denotes the bulb of a discharge tube with a reentrantstem 2 and a pinch or press 3. The tube contains an anode 4, a grid 5and a cathode 6. The latter consists of a cathode body 7 which may beconstituted, for example, by a nickel tube which is coated with astrongly electron emitting layer, for example with barium oxide andwithin which is located the heater which may consist, for example, of ahairpinshaped wire of refractory material.

Figure 2 distinctly shows the shape the cathode body and the heater mayhave according to the invention. In this figure, '7 denotes again thecathode body and 8 the heater whereas at 9' and 10 is shown the shapewhich the cathode body and the heater may havein order to obtain asatisfactory functioning according to the invenion.

a support 11' and at its upper end to a support 11 (Figure 1-) which isconnected again to a rod of glass or other insulating material 12. Inthis rod are mounted, in addition, the supporting rods 13 of the grid,the rod itself being secured to the anode. The leading-in wires 14 and15 of the cathode heater, the leading-in wire 16 of the cathode body,the leading-in wires 1'? and 18 of the grid and of the anode are led outof the tube through the'pinch or press 3. v

In the embodiment shown in Figure 5 the oathode sleeve 7 is shown ashaving the same form as that-shown in Figure 2, but the internal heaterelement; 8 is of such construction, as above described, that thoseportions thereof such as 9' and 10' which are in the neighborhood ofpoints of support of the cathode with supports 11 and 11! are of ,higherresistance per unit of length The cathode body is secured at its lowerend to than other heater portions that are not in the neighborhood of acathode support.

It is evident that although in the embodiments shown by way of example adetermined construction of the cathode body and of the heater is shown,it is to be understood that it is capable of embodiment in other anddifferent forms without departing from the spirit and scope of theappended claims.

For example, the invention is applicable to dischargetubes comprising anoblique or horizontal electrode system or to discharge tubes comprisingmore than one electrode system or a plurality of electrodes fulfillingthe same function.

Whatwe claim is:

1. An indirectly heated cathode for an electron discharge tubecomprising an electron emitting element, a heater adjacent to andsubstantially coextensive with said emitting element, and a supportconnected to said emitting element, the resistance of that portion ofthe heater which is'adjacent the point of connection between support andelectron emitting element being greater than any other equal portion ofthe heater.

2. An indirectly heated cathode for an electron discharge tubecomprising an electron emitting element, a support connected thereto,and a filamentary heater of the hairpin type adjacent, to andsubstantially coextensive with said emitting element and of uniformresistivity except for that portion which is adjacent the point ofconnection between support and electron emitting element which has ahigher resistivity than all other equal portions of the heater.

LODEWYK HENDRIX JONKER. MARINUS VAN GESSEL.

J OHAN KAREL

